2. Particle matters
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Solutions and suspensions P.5 of 13 
What does dissolve mean?
A solid dissolves in a liquid when it mixes completely with the liquid. The solid has broken down into pieces so small that its particles spread all through the new mixture. The solid and liquid will stay mixed without shaking.

The original solid breaks apart into pieces not much bigger than a few atoms or ions.

Particles dissolving
Picture 2.5 Sodium chloride in water: The moving water particles attach themselves to the solid particles and drag the ions away to form a solution.

What special words are used when talking about dissolving?
The substance that is dissolved is the solute. It dissolves into the solvent (often a liquid), to form a solution.
What happens when salt dissolves?
Salt is an ionic compound - sodium chloride (Na+ ions and Cl- ions).

Step 1. The moving water particles attach themselves to the solid particles.
Step 2. The water molecules drag the ions away - because they are moving.
Step 3 The ions go into solution.

Photos immiscible liquids

Water as a solvent
Water is a good solvent - especially of ionic compounds like salt (sodium chloride). We say that sodium chloride is soluble in water.

However, sand will not dissolve in water. It is insoluble.

What about other liquids?
Often water will not mix with molecular liquids like oil. We say that the two liquids are not miscible. They do not mix together or dissolve - they form two separate layers.

They have to be shaken up to get them to mix for just a short time.

Picture 2.6 Oil and water don't mix. They are immiscible. They form two separate layers. Shaking them will mix them for a short time.
Photos suspension

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What is a suspension?
A suspension is different from a solution. The solid particles have not dissolved but are suspended in the liquid. Suspended literally means that they are being held up or supported.

The individual pieces of solid are much smaller than the eye can see. However, unlike a dissolved solid, each piece has lots and lots of atoms. They mix completely with the liquid. The liquid supports the solid pieces and stops them falling to the bottom. However, unlike a solution, the suspension may not stay mixed without shaking – after a while, the solid pieces might fall to the bottom.

The solid pieces can be separated from the suspension by passing it through a filter.

Picture 2.7 Deodorant aerosols contain a suspension. The deodorant is a solid suspended in propellant. The particles will begin to settle and eventually fall to the bottom. It needs to be shaken to reform the suspension.
Question 5
Look at the paragraph below. There are some words missing. In each case, choose the best word from the drop down list. Then click on the 'Show answers' button to see how well you did.
A is a substance that dissolves in a to form a . It is broken into particles with only a few atoms.

Salt is in water whereas sand is .

Summary                                           Close
  • a solution is a complete mixture of (usually) a solid in (usually) a liquid
  • the solid particles are broken down into pieces a few atoms big
  • a suspension is larger lumps of solid floating in a liquid